The invention relates to a bulk material cooler having a cooling grate which carries the material to be cooled, such as hot cement clinker, and which conveys the material to be cooled from the material charging end to the material discharging end while a flow of cooling gas flows through said material to be cooled.
Grate coolers are used in the non-metallic minerals industry in order to drastically cool the material, such as cement clinker or other minerals, previously fired in a kiln, immediately afterwards on the cooling grate. For conveying the hot material to be cooled over the cooling line, the use of reciprocating grate coolers is particularly common, the grate system of which coolers comprises multiple alternately fixed and moving grate plate carriers, on each of which multiple grate plates are fixed, which are provided with cooling air apertures and which have a basically upward flow of cooling air passing through them. At the same time, viewed in the conveying direction, rows of fixed grate plates alternate with rows of reciprocating grate plates, which by way of their correspondingly reciprocating grate plate carriers are fixed to one or more driven reciprocating frames supported so that they can move longitudinally. The hot material to be cooled is gradually conveyed by the common oscillating movement of all moving rows of grate plates and is cooled in the process.
As an alternative to the aforementioned conventional reciprocating grate cooler, EP-1 021 692 B1 discloses a type of grate cooler in which the cooling grate with a flow of cooling air passing through it is not moved but is fixed, multiple rows of adjacent, reciprocating bar-shaped reciprocating elements being arranged above the fixed grate surface transversely to the conveying direction of the material to be cooled, said elements being moved between a forward stroke position in the material conveying direction and a return stroke position, so that the material is progressively moved from the beginning of the cooler to the end of the cooler by the reciprocating movement of these reciprocating elements in the bed of material to be cooled, cooling the material in the process. In a similar known type of grater cooler disclosed by DE 100 18 142 A1 the reciprocating elements moving above the fixed cooling grate base are divided into at least two groups and the reciprocating elements are moved forwards together in the conveying direction, but are moved backwards separately from one another rather than together.
In these known types of grate coolers the conveying capacity is decisively influenced by the difference between the volume of cement clinker moved by each forward stroke in the conveying direction and the volume of clinker undesirably moved counter to the conveying direction by the return stroke movement. In addition, in these known types of grate cooler the cross bar-shaped reciprocating elements are fixed on top of vertical drive plates oriented in the longitudinal direction of the cooler, which extend through corresponding longitudinal slots in the cooling grate and are driven from beneath the cooling grate, making it relatively expensive to seal off the cooling grate, charged with material to be cooled, to prevent material falling through the drive plate apertures, and thereby to keep the material wear within bounds. The reciprocating elements moved in the hot cement clinker bed are exposed to a high level of thermal and mechanical wear, reducing the service life of the grate cooler. Finally the hot bed of bulk material is intermixed by the reciprocating elements moved in the bed of material, which has a detrimental effect on the thermal efficiency of such types of grate cooler.
In addition, DE 196 51 741 A1 discloses a cooling tunnel for cooling and/or freezing material to be cooled by means of cold air, using a so-called “walking floor” conveying principle, in which multiple adjacent floor elements of the cooling tunnel are moved forwards together in the conveying direction but are moved back separately from one another rather than together. The intention is to form a high bulk material bed over the floor elements, which fills the entire cooling tunnel cross section, so that the cooling gas flows through the progressively advancing bulk material in the opposite direction. The actual floor elements remain uncooled by the cooling gas, so that the known cooling tunnel would be unsuited to cooling red hot cement clinker falling from the discharge end of a rotary kiln. The direct contact of the hot cement clinker with the surface of the floor elements would mean exposure to a high level of thermal and mechanical wear and in the case of hot cement clinker would therefore lead to an inadequate service life of such a cooling tunnel. Furthermore, the adjacent floor elements of such a cooler could not be used with a long length of 40 to 50 m, for example, such as industrial grate coolers need in terms of their throughput capacities and cooling line lengths for the cooling of hot cement clinker.